What it is
Mostly water — commercial brands run about 2% almonds, roughly four nuts a cup — suspended with gums and fortified to look like it has the nutrition of milk.
Why your biology objects
At 2% almonds it delivers around 1g protein a cup against milk's 8g; it's fortified water with a gum holding the few solids in suspension. Harmless as a low-calorie drink, but it's an engineered impression of a food, not the food. (Carrageenan versions earn the heavier flag — see that line.)